弹性流体动力润滑状态下滚动轴承摩擦的分析

基于非牛顿弹性流体动力润滑(弹流润滑)点接触问题的数值求解方法,对深沟球轴承滚动体与滚道椭圆接触的稳态与瞬态润滑问题进行了分析.依据油膜压力与油膜厚度的数值计算结果,讨论了接触表面粗糙度、表面几何形态(粗糙表面峰谷高度)、滑滚比、接触力以及滚动速度等参数的改变对润滑深沟球轴承摩擦系数的影响.结果表明:表面粗糙度的改变对摩擦系数的影响较小;粗糙度一定时,表面几何形态的差别对摩擦系数影响较小;摩擦系数随着滑滚比的提高而增大;接触力与滚动速度的提高导致摩擦系数增大.     

薄壁零件铣削三维颤振稳定性建模与分析

以低刚度薄壁零件为研究对象,基于加工原理建立精确的铣削过程薄壁零件三维动力学模型,并在此基础上采用全离散解析法对颤振稳定域叶瓣图进行仿真分析及实验验证.结果表明:薄壁零件铣削加工系统的动态特性决定其动力学模型,铣削加工过程主轴转速与颤振临界轴向切削深度之间存在非线性关系,主轴转速对颤振稳定性影响较明显.当系统模态质量、阻尼比及固有频率增大时,颤振稳定性相应加强,同时叶瓣图形状分布随之改变.该理论模型对薄壁零件铣削加工过程切削参数的合理选择,表面加工质量和加工效率的提高具有一定指导意义.     

基于蒙特卡洛法的铣削让刀误差概率分布预测

基于斜角切削理论,建立铣削力计算模型,求解得到铣削力.构建薄板受力变形的挠度函数,结合刀具的受力变形求解刀具-工件耦合变形的铣削让刀误差.采用神经网络拟合方法,求出输入铣削参数与输出最大让刀误差的函数关系.考虑刀具参数、材料参数、工件参数以及加工工况等随机参数对金属切削的影响,利用蒙特卡洛方法,对输入参数进行抽样,将参数样本代入神经网络拟合的函数模型中,获得铣削让刀误差样本,并分析其概率特性,从而提出一种铣削让刀误差的概率分布预测方法,较确定性计算铣削让刀误差的方法更加符合实际.     

钛合金螺旋铣孔参数对表面粗糙度影响研究

螺旋铣削作为一种新工艺在钛合金制孔方面得到广泛应用,表面粗糙度是评价钛合金孔加工质量的重要指标。基于Matlab建立钛合金螺旋铣孔表面粗糙度预测模型,开展钛合金螺旋铣孔实验,研究发现:在0.15~0.25 mm/rev范围内,随着螺距的增大,钛合金孔表面粗糙度呈现先减小后增大的变化趋势;在0.03~0.05 mm/tooth范围内,随着切向每齿进给的增大,表面粗糙度呈现先逐渐增大后减小的趋势;类似的,在2 500~3 500 r/min范围内,随主轴转速的提高,表面粗糙度变化曲线呈现先升高再降低的规律,但之后又有平缓上升的趋势。研究结果可为钛合金螺旋铣孔参数优化及表面粗糙的控制研究提供重要实验依据。     

Application of X-ray diffraction, micromagnetic and hole drilling methods for residual stress determination in a ball bearing steel ring

A basic understanding of distortion problems requires the analysis of a complete manufacturing process including an almost complete overview of residual stress states in the component during each production step. To reduce the measurement time in the future, three measurements methods (X-ray diffraction, micromagnetic and blind hole drilling methods) have been used to analyze residual stress states in machined AISI 52100 ball bearing rings. X-ray diffraction was used as a state-of-the-art method for machining induced residual stresses with pronounced gradients. The ring exhibited a complex residual stress state with high tensile residual stresses at the surface, a strong gradient in depth, and also showed some variation along the outer circumference due to a superimposition of machining induced residual stresses and effects from the clamping device process. Due to this surface state, micromagnetic signals depend on the analyzing frequency. A calibration of the signals was only possible with the X-ray diffraction data. The results of the three different measurement methods correlate reasonably well.     

Synthesis of boron suboxide (B6O) with ball milled boron oxide (B2O3) under lower pressure and temperature

Boron reacted with ball milled boron oxide under pressures between 1 and 5 GPa and at temperatures between 1300 and 1700 °C to afford boron suboxide (B₆O). Icosahedral B₆O grains with diameters ranging from 100 nm to 1.3 μm were prepared. The factors that affect the synthesis of B₆O are investigated. The best sample with crystal size up to 1.3 μm is obtained at 2 GPa and 1400 °C for 6 h. The indentation experiment gave an average Vickers hardness of 32.3 GPa for bulk B₆O sample, which is consistent with previous reports. Bulk B₆O sample exhibits oxidation resistance in air up to 1000 °C and mild oxidation in the temperatures of 1000-1200 °C, which is more oxidation resistant than diamond. It is possible that B₆O could be used as a substitute for diamond in industry because of its relatively mild synthesis conditions, high thermal stability and high hardness.     

On the Bergman representative coordinates

We study the set where the so-called Bergman representative coordinates (or Bergman functions) form an immersion. We provide an estimate of the size of a maximal geodesic ball with respect to the Bergman metric contained in this set. By concrete examples we show that these estimates are the best possible.     

一种离轴凸双曲面单修加工及检测方法的研究

离轴凸双曲面的加工和检测是非球面加工检测中的一个比较困难的问题.结合一块口径φ230mm、离轴量226mm的凸双曲面镜,提出了离轴凸双曲面镜单修加工以及采用离轴Hindle球检测偏转角度的离轴凸双曲面镜这一方案.给出了单修加工工艺,并解决了检测光路的搭建难点.加工完成的离轴凸双曲面的面形精度RMS优于λ/50(λ=63...     

Quadrangulations of sphere and ball quotients

We give a classification of sphere quadrangulations satisfying a condition of non‐negative curvature, following Thurston's classification of sphere triangulations under the same condition. The generic family of quadrangulations is parametrized by the points of positive square‐norm of an integral Gaußian lattice in the six‐dimensional complex Lorentz space. There is a subgroup of automorphisms of acting on this lattice whose orbits parametrize sphere quadrangulations in a one‐to‐one manner. This group acts discretely on the corresponding five‐dimensional complex hyperbolic space; is of finite co‐volume; its ball quotient is the moduli space of unordered 8 points on the Riemann sphere, and also appears in Picard‐Terada‐Deligne‐Mostow list. Both Thurston's lattice and our lattice may be thought of as parametrizations of certain families of subgroups of the modular group; equivalently, of certain families of dessins. These families also parametrize points of a moduli space.     

数控雕铣加工铝合金材料进给速度的优化与实验验证

针对数控雕铣机床加工铝合金件的特点,运用多目标优化理论,建立了加工成本与加工效率的数学模型.经过计算,得到了一系列的进给速度的优化解.经过实验加工和验证,最终得到了在该条件下较为理想的进给速度取值范围(Vf∈2 400～2 560 mm/min).研究表明,以该进给速度范围进行加工铝合金材料时,能够以相对较低的加工成本和较高的效率得到良好的表面质量.